Hydrophone for directional listening buoy



Ju'ne 1s, 1959 H. 0. BENECKE HYDROPHONE FOR DIRECTIONAL LISTENING BUOY Filed June 28, 1955 INVENTOR.

' HEINRICH o. BENECKE ied States Pate The invention described 'he'reinmay be manufactured amused b error the-Gever'nmepr-df uie fUn'it'e'd States of Ame r'ia'for' 'goyernnienfal purposes without"the/payment of any royalties thereon or therefor.

This iiivntio'n'relates to transducers, gramme particunay to a directional hydrophdne 'of sinall dimensions capable ofdetecting underwater sound "so elfectively that it is well suited "for use in a listening buoy "of restricted "size.

1-11 existing equipment for underwater search including the type known as listening buoys, transducers o'r hydrophon e's are incorporated as sauna detectors 'for use in locating underwater targets whi'ch characteristically generase sounds capable of detection by this means.

The accuracy and range of transducers used as directional underwater sound detectors in such equipment is geveraed by a number of factors of which the attenua- 'ti'o'rl of sound waves in water and the directivity of the equipment used are mest impona t. Henca both of th''s factors must be dp'tiifiized Within the: practical restneaea or limited given dimensions for the equipment.

The range is adversely afiected by atteflliati'oii ofthe sound waves in water which decreases with dec easing frequency, so that attenuation is niiniiniz 'ed by the use of a low operating frequency. the other hand, the dire'ct'ivity, which ravdtauy streets" the range, increases; for equipmentof giveii dimensions, with increasing frequency, so that directivity is achieved byth'e use of a high operatin frequency. Moreoye'r; accuracy at the e uipment' is em c'ed' by a narrow beam and hence by use of a high operating frequency to increase d'i'r'ctivity, but the narrowest possible beam is not most desirablefor the use indicated above, since' the beam should b'e sufficien'tly wine to eliminate errors due to refraction and to prd ide a" su'fiicient time on target for the ound sensitiv beam as the portion of me'equi ment supporting the transducer is r'otated through 360' about a vertical a'xis'in' the course of conventional operationof equipiheiif inorpor'ating direeueuar sounddetectors for underwater search: Thus, it is necessary in designing the device characteriii'ng" the instant invention-to properly reconcile all of thesefactors it? selecting the-operating frequency tooptirnize the range and accuracy ofthis device. t

With respect to the'physical" dimensions of. the equipment; both-range and: accuracy have a tendency to increase with'increased diinensions. However, thepraetical size-of-suchequipment is narrowly restricted by the severe limitations as to space and weight characteristic of all airl borne equipment. Qonsequently, the problem, arises. of making-the-best possible useof the'limited space available byselectin'g jthe'lmost' eflfective' arrangement of the sound" sensitive elements nemesis "the fequipment, For example, the diam'et r 'ofjthdstandard launching tube installations" presently used for' launching" listening buoys rmmaneran dictatestheiniairinaumpractical diameter for a"rigidtrar'1sduceiassernb 1' In thepast,'-attempts" have been made to meet the practical: "operating" requirements of transducers used as directional underwater sound de- 1 2,891,232 Patented, 16, 1.959

,'2 tectors as well as the space limitations noted above by a. construction which provided :for 1 'anSdt1 ccr assemblies which would fold into arconfigurati'on-fit-ting into the launching tube and would untoldafter 'launchingthrough the tube ,into ;an. extended configuration et; substantially larger overall dimensions to provide the desired directivity of about 30. This expedient is subject to. the disadvantages that the added mechanical structure necessary for articulation of thev assembly to provide for extension-of certain parts after water entry increases the possibility of mechanical failures and that the extendedjconfiguration impedes'rotation of the assembly underwater at the same time it renders the transducer moresubject totilting caused byv local currents whichgreatly reduces accuracy. 1 r

I, vIt is, therefore, an objectof this invention, to, provide of about 30?v and containedwithin the overalldimensions of former transducers in their collapsed non-operating cons a onw 1 v 1 r Y, ,It is ;a further object of this invention to'provide a transducen as, stated above, which is pf simplified construction and contains a minimum of relatively movable mechaniwo napa t e I 1 1 1.

lt hasheen ,foundtthat thegbove and other objects of t s invent on a a c mp ished by-1av ra s u er unit, in w ic thetran du e e eme a sp e apart a distance equ lto n r a f tl w vc le st jq e t a sm tmgirequ n y a a e spacedadis an r ;a.p1a a e c in surface equal to one-fourth the Wave length of the transt in -freq enc s. v, h nv ntion m stre di i' aders ocd, yireference at f low n e r p i a the aQce na-ny n drawsh cby m de a pa t fi a rr ca iq ran Qu:;whi h: Fig. 1 is. afront yiew ofithe'preferred embodiment of ea s u q he stant ren ien, 1. ,1 it,

, Fig, 2 11s a horizontal cross-section taken on the line i i I r i ,Fig. 3 s a q all ressrs c o r o amqdifi at-io f thisinvention shaped to fit into a launching tube of given IIl I I, d?-... r 1;: a -.::;ii; 1:,

,Eig, 4 isa;horizontalcross-section of another modificanoffl i ent on .fr .9 lam? f 1:31;:2;

-,In the various figures, lik e reference numerals'designate likeiqn corresponding-penn Rd na r o isth n l n rd en c larg -w t e pect-lo the o er linear dimensions, and, accordingly, are referred to herein as linear transducers, V v I 11.1 As how-si B -24 3a,, re s ndr transducer elements 10 are spaced apart a distance of measured perme ting; centerswhere X is the wavelength in water of the operating f reqnencyl The transducer elenients'flfl are :inour'itet' lparallel to each other in the same plane and have diameters such that their outer surfaces are spaced apart. A reflector 13 mounted between plates 11 and 12 provides a planar reflecting surface 14 located a distance from the axes of the transducer elements. The reflector 13 is of a material having a specific impedance much less than that of water. A suitable material for the reflector is rubber having entrapped air enclosures therein.

In operation the transducer assembly illustrated in Figs. 1 and 2 is incorporated in conventional equipment for underwater search by aircraft, including, for example, a radio link and auxiliary orienting devices. In searching, the transducer assembly incorporated in such equipment isf r3o6t3ted about a vertical axis, usually through an arc The embodiment of Figs. 1 and 2 was made to operate at a frequency of about 15 kilocycles and was in fact constructed as part of a listening buoy having a circular cross-section, as shown in Fig. 3, to be launched from a launching tube having an inside diameter of 6% inches. The operational frequency of 15 kilocycles employed in this modification was found to be practically optimum. The horizontal angle of the beam was between 25 and 30 degrees. It was found that the described spatial relationship between the transducer elements as respects each other and as respects the elements and the reflecting plane in terms of wave length gave results of range and ac curacy equal to that given by much bulkier transducers of previously known types. Although the described modification includes four transducer elements, the principle of building space saving transducers taught herein is not restricted to this number.

Referring to Fig. 3, in this modification, the transducer assembly is shaped to fit inside a standard launching tube of specified diameter by making the base plate 11 and top plate 12 circular. As shown in Fig. 3, one-half of the area of the base plate 11 is unoccupied, while the four transducer elements illustrated form a complete transducer assembly. This illustrates that the invention exceeds the objective of providing a transducer assembly within the dimensions of conventional transducer assemblies in that only one-half the space available within standard launching tubes is used. Consequently, the space saved can be utilized in several ways. For example, it may be used to accommodate a second transducer with identical performance characteristics in order to give additional information, as shown in Fig. 4.

The modification illustrated in Fig. 4 in a view corresponding to that in Fig. 3 includes two identical transducer assemblies mounted on opposite sides of the reflector 13 having two planar reflecting surfaces 14 and each including a plurality of transducer elements 10 arranged according to the critical spatial relationship specified above in describing the embodiment of the instant invention shown in Figs. 1 and 2 above. With two transducer assemblies mounted as shown in Fig. 4 so that they are opposed 180", twice the number of informations per unit time may be obtained without recourse to increased rotational speed. Alternatively, the same number of informations per unit time may be obtained at half the rotational speed. Yet, the modification illustrated in Fig. 4 can still be accommodated within the space available in a standard launching tube.

It should be understood that the number of transducer elements included in the various embodiments of the instant invention is exemplary only and that the number of such elements may be varied as necessary under varying operating conditions or to satisfy different operating requirements. Likewise, the length of the transducer elements is determined by specific design requirements established to insure optimum results in various applications of the instant invention. Finally, the reflector 13 may consist of thin sheet material stretched taut between plates 11 and 12 to form planar reflecting surfaces 14.

' teachings.

The spatial relationship of the respective transducer elements within all of the disclosed modifications of this device was found to produce the highest efliciency with respect to range and accuracy when compared to any other arrangement within the same overall dimensions. Moreover, since the transducer assemblies of this invention eed not be extended to greater overall dimensions after they are launched, they have a minimum of relatively moving parts subject to mechanical failures. Finally, the complete absence of protruding elements of the type found in prior devices used for directional underwater sound detectors permits rotation by application of a smaller torque and renders this invention less subject to the unbalanced forces imposed on such a device by water currents and waves.

Obviously, many modifications and variations of the present invention are possible in the light of the above It is, therefore, to be understood that within the scope of the appendedclaims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. An electro-acoustic sound receiver assembly comprising a plurality of sound receiver elements disposed parallel to each other in a common plane and spaced apart a distance equal to one-half the wavelength of a predetermined operating frequency, and a planar sound reflector disposed parallel to the common plane of said sound receiver elements at a distance equal to one-fourth the wavelength of the predetermined operating frequency.

2. An electro-acoustic underwater sound receiver assembly comprising a plurality of like elongated sound receiver elements disposed parallel to each other in a common plane and spaced apart a distance on centers equal to one-half the wavelength in water of a predetermined operating frequency, and a planar sound reflector disposed parallel to the common plane of said sound receiver elements and spaced therefrom a distance equal to one-fourth the wavelength in Water of the predetermined operating frequency.

3. An electro-acoustic underwater sound receiver as-' sembly comprising a plurality of elongated cylindrical sound receiver elements of substantially equal length, a first supporting means fixedly interconnecting the respective elements at one end, a second supporting means fixedly interconnecting the respective elements at the other end, said elements being arranged with their respective longitudinal axes disposed parallel to each other in a common plane and spaced apart a distance equal to onehalf the wavelenth in water of a predetermined operating frequency, and a reflector member extending between and connected to said first and second supporting means, said reflector member having a planar sound reflecting surface disposed parallel to the common plane of the longitudinal axes of the respective sound receiving elements and spaced therefrom a distance equal to one-fourth the wavelength in water of the predetermined operating frequency.

4. An electro-acoustic transducer assembly for use underwater comprising a plurality of elongated cylindrical transducer elements of substantially equal length, a first supporting means fixedly interconnecting the respective transducer elements at one end, a second supporting means fixedly interconnecting the respective transducer elements at the other end, said transducer elements being arranged with their respective longitudinal axes disposed parallel to each other in a common plane and spaced apart a distance equal to one-half the wavelength in water of a predetermined operating frequency, and a reflector member extending between and connected to both said first and said second supporting means, said reflector member having a planar sound reflective surface of a low specific sound impedance disposed parallel to the common plane of the longitudinal axes of the respective transducer elements and spaced therefrom a distance equal to one-fourth the wavelength in water of the predetermined operating frequency.

5. An electro-acoustic transducer assembly for use underwater comprising a plurality of elongated cylindrical transducer elements of substantially equal length, a first fiat circular supporting means fixedly interconnecting the respective transducer elements at one end, a second flat circular supporting means fixedly interconnecting the respective transducer elements at the other end, said transducer elements extending perpendicular to both of said supporting means with their respective longitudinal axes disposed parallel to each other in a common plane and spaced apart a distance equal to one-half the wavelength in water of a predetermined operating frequency, and a reflector member extending perpendicularly between and connected to both said first and said second supporting means, said reflector member having a planar sound reflective surface disposed parallel to the common plane of the longitudinal axes of the respective transducer elements and spaced therefrom a distance equal to onefourth the wavelength in water of the predetermined operating frequency.

6. A device as described in claim 5, in which said reflector member is located diametrically of said first and second circular supporting means and has a second planar sound reflecting surface on its opposite side, and, in addition, a second equal plurality of elongated cylindrical transducer elements fixedly attached to said first and second supporting means on the other side of said reflector member, said second plurality of transducer elements extending perpendicular to both of said supporting means with their respective longitudinal axes disposed parallel to each other and spaced apart a distance equal to onehalf the wavelength in water of the predetermined operating frequency in a second common plane disposed parallel to said second sound reflecting surface and spaced therefrom a distance equal to one-fourth the wavelength in Water of the predetermined operating frequency.

7. In combination with transmitting, receiving and orienting apparatus therefor, an electro-acoustic transducer assembly for use underwater, comprising at least one set of four elongated cylindrical transducer elements of substantially equal length, a first supporting means fixedly interconnecting the respective transducer elements at one end thereof, a second supporting means fixedly interconnecting the respective transducer elements at the other end thereof, said transducer elements being arranged with their respective longitudinal central axes disposed parallel to each other in a common plane and spaced apart a distance equal to one-half the Wavelength in Water of a predetermined operating frequency, and a reflector member extending between and connected to both said first and said second supporting means, said reflector member having at least one planar sound reflective surface of a low specific sound impedance disposed parallel to the common plane of the longitudinal axes of the respective transducer elements and spaced therefrom a distance equal to one-fourth the wavelength in Water of the prede' termined operating frequency.

References Cited in the file of this patent UNITED STATES PATENTS 1,277,562 Fessenden Sept. 3, 1918 2,095,083 Renatus Oct. 5, 1937 2,313,513 Brown Mar. 9, 1943 2,511,689 Beechlyn June 13, 1950 

